Plugging uncased wells



Dec. 27, 1955 s. c. HOWARD PLUGGING UNCASED WELLS Filed Feb. 27, 1952 GEORGE C. HOWARD IN VEN TOR.

AT TORNE Y United States Patent PLUGGING UNCASED WELLS George C. Howard, Tulsa, Okla assignor to Stair-slim! Oil and Gas Company, Tulsa, 01th., a corporation of Delaware Application February 27, 1952, Serial No. 273,665

7 Claims. (Cl. 166-22) This invention pertains to the art of plugging uncased wells. More particularly, this invention pertains to an improved method for preventing fluid from by-passing around a plug set in an uncased well. This application is a continuation-in-part of my application Serial Number 203,654, filed December 30, 1950, now abandoned.

In the arts of selectively treating and selectively analyzing a part of the formations penetrated by the well, it is often desirable to isolate selected zones of uncased wells from the remainder of the well. Examples of operations involving such isolation are: selective acidizing, squeeze cementing, plastic or other selective plugging, formation sampling, formation testing, logging points of fluid ingress in a well, and the like. Various open-hole or formationtype packers have been proposed for plugging open holes. Cement plugs have been used for the same purpose. In general, it is found that open-hole packers are not effcctive in preventing fluid migration from a high-pressure area to a low-pressure area in a well. Several explanations have been advanced for this fact. Among these are the facts that cement shrinks on setting, that an uncased well usually is not cylindrical and hence cannot be perfectly fitted by a cylindrical packing, and the fact that such plugs are often set in rocks having, in general, the same permeability as the surrounding producing formations.

It is therefore an object of this invention to provide an improved method of isolating a zone penetrated by an uncased well. A further object of this invention is to provide a method of sealing a formation packer which will prevent fluid communication between the high-pressure and the low-pressure sides. It is a more specific object of this invention to provide a means of sealing the flow channels around a formation packer to prevent fluid communication between thehigh-pressure and the'lowpressure sides of a formation packer. Other objects of this invention will become apparent from the following description in which:

The figure is a diagrammatic representation of the apparatus used in isolating a selected zone of a well from the remainder of an uncased well.

The invention comprises, in brief, the sealing of flow channels around a formation packer, both in the well and in the permeable formations contiguous to the well, by filling such flow channels with a sealing agent comprising a hydrocarbon gel or a slurry of a temporary bridging material in a gel or low-penetrating liquid. Such materials cannot easily be moved when fluid pressure is applied across a packer but can subsequently be removed by'contact with a suitable gel breaker.

Referring now more specifically to Figure 1, a partially cased-well 10 extends through three permeable formations, an upper formation 11, a selectedformation 12 which is to be treated or tested, and a lower formation 13. Well 10 is uncased throughout these three permeable formations. As customary, however, the well is equipped with an oil string or casing 14 which may have been cemented to prevent fluid migration behind'the casing.

2,728,395 Patented Dec. 27, 1955 At the surface, means are provided for injecting fluid into the casing through a tubing head 15. The tubing head also supports a tubing string 16 on which a treating or testing tool 17 is suspended. The tool is represented as a so-called straddle packer-i. e., a packer adapted to straddle a selected formation which is to be tested or treated. However, as shown hereinafter, a tool having one or more packers could be sealed by the same process. The tool consists of an upper packer 18 and a lower packer 19. For convenience the packers are shown as simple packing elements but in practice these are typical expanding formation packers. The packing elements or plugs may be of any flexible material, such as leather, webbing, rubber, or the like, or they may comprise settable materials such as cement, plastic, or the like. The packers are mounted axially upon a tubular framework or arbor 21 which may be varied in length, depending upon the thickness of the selected formation receiving treatment. The arbor is provided with perforations 22 between the packing elements whereby fluid may be injected through the tubing into the isolated zone 23 of the well and forced into selected formation 12. 0bviously, when the apparatus is used for isolating production from the selected formation, as, for example, when the apparatus is used for determining the character of fluids produced from the selected formation 12, fluid enters the tubing through perforations 22 and then flows or is lifted to the surface. In the case of a straddle packer, as shown, it is generally desirable to provide a fluid by-pass 24 between the section of the well above the upper packer and below the lower packer. The mandrel 21 is plugged at the lower end, so that the only fluid communication between the formation and the tubing is through the arbor perforations 22.

At the surface, the annular space 25 between casing 14 and tubing 16 is connected to a supply of a low-penetrating gel or packer sealing agent (not shown). A pump 26 is provided to displace the sealing agent into the well. The upper end of the tubing is connected with a supply of treating agent, such as acid, cement, plastic, or the like (not shown), and a pump 27 is provided to force this treating agent into the tubing and thence into the selected formation 12.

The low-penetrating liquids or gels used to seal the flow channels around the packing element are preferably oily or hydrocarbon gels. The base liquid or solvent is, for example, a higher alcohol, crude oil, or a refined oil such as gasoline, kerosene, naphtha, fuel oil, diesel oil, or the like. This base liquid is gelled with an oil-soluble gelling agent, such as grease-making soaps produced by or from ammonia or any material of the alkali-metal and alkaline-earth-metals groups and some polyvalent metal groups including sodium, potassium, magnesium, calcium, strontium, cadmium, mercury, lithium, cobalt, lead, nickel, combined with a fatty acid. A desirable gelling agent is made from aluminum soaps or a combination of aluminum soaps, particularly a 2:1:1 mixture of aluminum soaps of coconut oil acid, aluminum naphthenate, and aluminum oleate. This mixture of aluminum soaps has been used in the preparation of compositions for flame throwers and-incendiary bombs, is known by the name of napalm, and has been described in detail in an article entitled Napalm, Industrial and Engineering Chemistry. Industrial Edition, vol. 38, No. 8, August 1946, page 768. From about 3% to about 10% of this soap by weight is dispersed in the base liquid. The amount of soap depends somewhat upon the base liquid. In general, a higher percentage of soap is required in the heavier hydrocarbons. In any case, the amount of soap is 'sufiicient to produce apumpable gel having a viscosity greater than about 500 centipoises and preferably greaterthan about 50,000 centipoises, as measured on the Halliburton Thickening Tim'e Tester described in API Code 32, paragraphs 50-62 inclusive.

In some cases, it is desirable to include in the gel a delayed-action peptizer, such as water or the lower alcohols. For example, from about 0.1% to about 3%, typically about 1%, by volume of the peptizer may be incorporated in the gel by emulsification or the like. This peptizer appears to shorten the time required for the gel to reach maximum viscosity and, after several hours, to reduce the gel to a sol having a viscosity substantially equal to the viscosity of the base liquid.

In the preferred embodiment, bridging materials are added to this low-penetrating liquid. Bridging materials are well-known in the drilling fluid art where, as is wellknown, these solid particles are used to regain circulation. Bridging materials fall generally into one of the following three classes: (1) fibrouspliable, stringy materials which tend to entangle or mat over a pore or crevice; (2) granular-angular, rigid materials which tend to bridge against each other in a crevice without being distorted appreciably; and (3) lamellated-materials formed of thin sheets or flakes. The particle sizes of each of these materials vary over wide ranges, but in general it can be said that the particle size is substantially above the colloidal range (3000 mesh, theoretical, or smaller) and above the slimy or smooth and non-gritty range (200-3000 mesh). Granular bridging materials, for example, may have a particle size from about maximum dimension down to 100 mesh U. S. sieve. Lamellated and fibrous materials may have a maximum dimension in the range ,4 to l" or thereabout. These materials are sufficiently rigid and of sufiicient size to bridge in a fracture or on the surface of the fracture and form a framework which prevents flow' of the low-penetrating liquid into the fracture.

Bridging materials of any of the above types may be used provided, however, that the bridging material, especially the smaller particles, must be of a temporary nature, i. e., these particles must be capable of being removed from the fractures and from the well. For this reason, I prefer (I) a bridging material which melts at formation temperature after a suitable delay, (2) a bridging material which melts above the formation temperature and is removed by a hot solvent, or (3) a bridging material which is dissolved within the formation as by an extraneous liquid such as acid or is dissolved by fluids indigenous to the formations. Among the bridging materials which are temporary and which can be removed from a formation are a number of the harder waxes which may be flaked or granulated at atmospheric temperature such as yellow beeswax, carnauba wax, shellac wax, sugar cane wax, or microcrystalline hydrocarbon waxes. Fats and hardened oils, for example, highly hydrogenated oils including animal oils, vegetable oils such as soy bean oil, cotton seed oil, or the like, and mineral oils such as cup greases or the like, are also contemplated. Some of the coal tar derivatives such as phenol, naphthalene, diphenyl, acenaphthene, fluorene, phenanthrene, anthracene and the chlorinated coal tar derivatives such as paradichlorobenzene or pentachlorophenol are quite satisfactory, being solid at atmospheric temperatures and being soluble (dissolve or sublime) in well fluids such as methane and crude oil or melting within the range of typical formation temperatures. That is, depending upon the depth of formation to be treated a bridging material is selected which has a melting temperature very close to, but lower than, the formation temperature. The approximate formation temperature can be readily computed from the equation:

The concentration of the bridging material in the gel or low-penetrating liquid may be varied over a substantial range depending, among other things, upon the consistency of the low-penetrating liquid, the solubility of the bridging material in the low-penetrating liquid, and upon the size and shape and particle size distribution of the bridging material. I have found, for example, that a bridge will form in a crevice or pore more rapidly the higher the concentration of the bridging material. 0n the other hand, the maximum amount of bridging material which may be added is somewhat limited by the ability to pump the slurry. Using naphthalene as a bridging material, it has been found, for example, that after the lowpenetrating liquid has dissolved about 50 pounds per barrel of naphthalene, i. e., after the low-penetrating liquid is saturated with naphthalene, between about 200 and about 300 pounds may be added to a barrel, 42 gallons, of oily liquid having a viscosity in the range of about 3000 centipoises and that this sealing agent will seal the passages around a packer where the permeability of the formation is as high as a darcy or more or where there is a fracture as wide as about 0.1 inch.

It is desirable to provide a gradation of particle sizes in the bridging material, particularly the granular bridging material, since bridging appears to depend somewhat upon a statistical arrangement wherein the larger particles start a bridge in a crevice and this bridge is further extended by the bridging of smaller particles on the larger particles. Uniform granular particles of a size suflicient so that one particle bridges in a pore or crevice are not considered desirable since particles of this size have such a high permeability that the gel can be squeezed through the interstices of the solid particles building up a large deposit of bridging material in the well without ever plugging the pore or crevice. Accordingly, as indicated, the particle size of a granular bridging material is prefer ably a gradation of particle sizes between about 4 and about mesh U. S. sieve including particles in the intermediate range. It should be pointed out, however, that the main objective is that the larger particles bridge in the pore or crevice and that the smaller particles bridge on the large particles. The particles of intermediate size are not therefore always considered necessary.

In operation, after the packers have been set, the sealing agent as above described, including preferably the peptizer, is pumped into annular space 25 by pump 26. In a high-fluid-level well, the sealing agent is displaced down the well to the packer by pumping another liquid, such as oil or water, into the annular space on top of the sealing agent. Where there is a straddle packer, the sealing agent is displaced to the bottom of the well through by-pass 24, so that it covers the low-pressure side of both packing elements. The amount of sealing agent injected depends upon a number of circumstances, such as the diameter of the well, the type of packer, and the like; but, in general, enough sealing agent is injected into the well to fill completely the open-hole section plus an allowance for some penetration into the permeable formations and fiow channels less the volume of hole isolated by the packer or packers. After the sealing agent is spotted in the open hole and around the packing elements and the well fluids have been displaced into the permeable formations or otherwise removed from the well, the pressure on the displacing liquid as indicated by the pump discharge pressure commences to rise, since the viscous sealing agent does not readily penetrate the permeable formations. Pumping is continued until this pressure is built up to several hundred pounds. The pressure is maintained below the safe working pressure for the casing and below the pressure at which the formations might be fractured. This pressure causes the sealing agent to penetrate the pores of formation 11 and 13 and the flow channels around the packers, both in the well and in the formations, thereby plugging the flow channels. Desirably, the sealing agent is injected into the well before maximum gelation of the gel is reachedfor example, it is desirable to spot the sealing agent in the well at the time it has a viscosity of between about 25 and about 100 centipoises. Having a relatively low viscosity as compared to its maximum viscosity, it can more readily be pumped into the flow channels. With some of the gel in the flow channels, pumping is discontinued after a medium pressure is develop-ed. Gelation continues, so that the viscosity of the gel in the slurry which penetrates the flow channels may reach a viscosity as high as several poises.

While the viscosity of the gel is reaching its maximum, as indicated by a sample of' the sealing agent retained at the surface or by some other means, and preferably while pressure is maintained on the sealing agent, the treating solution, e. g., acid, is injected into the well through tubing 16. The treating'solution enters the confined zone 23 of the well through perforations 22. The pressure on the treating solution may then be built up by pump 27 to several thousand pounds, if necessary, to force the treating solution into the selected formation 12. This treating solution cannot by-pass packers 18 and 19 through the flow channels in the well around the packer or through the pores in the formations because these flow channels and pores have been plugged by the sealing agent. Any amount of treating solution may be injected into the selected formation without by-passing the packers, even though the sealing agent does not penetrate a substantial distance out into the permeable formations, since the major pressure drop, which often causes failure of open-hole packers, occurs very close to the well. Since the flow channels close to the well are plugged by the sealing agent and since pressure is maintained on the sealing agent, the tendency for the treating solution to return to the well around the packers is materially retarded. The treating solution therefore goes into the selected formations, even though extreme pressures are applied to the treating solution.

After the treating solution has been injected into the selected formation, the packers may be unseated and removed from the well. The gel in the sealing agent, as indicated above, may contain a delayed-action peptizer which causes it automatically to break and flow back into the well when the well is produced. Where the peptizer is not incorporated in the gel, as, for example, where the packer is to be sealed for several days, it may be injected into the well and placed in contact with the gel at any time to reduce the viscosity of the gel and assist in its removal from the pores of the formation. It appears that the bridging materials do not enter the pores and crevices to an appreciable extent so they are more readily removed from the well by melting, by solution, or the like, as above described. Among suitable materials for breaking or peptizing the soap hydrocarbon gels are the amines, ammonia, oil-soluble sulfonates, strong acids, or the like. One good gel breaker is dibutyl amine. The peptizer may be diluted with a suitable solvent, such as gasoline, before it is injected into the well. Generally, from about 0.5% to about 6% of the peptizer, typically between about 1% and about 3%, based upon the volume of the gel and the concentration of the gelling agent in the gel is incorporated in a volume of solvent equal to about the volume of the gel. This peptizer is allowed .to stand in contact with the gel for from several hours to a day or more to reduce the viscosity of the gel. After its viscosity has been broken, the sol flows from the formation into the well and is produced with the other fluids from the well.

While reference has been made generally to treating a selected formation in. a well, it will be apparent that the above-described process for sealing a formation packer or plug and isolating a selected formation is equally adapted to processes in which a fluid is withdrawn from selected formations-i. e., processes in which the pressure drop across the packer is in the opposite direction. The sealing agent in the flow channels around the packers, in such application, prevents flow of fluids from the surrounding areas past the packer into the isolated zone of the well. Accordingly, under this latter embodiment the flow properties, character of fluid produced from a 6 selected formation, or the-like can be determined with greater accuracy.

From the foregoing it can be seen that thisinvention is susceptible to a great variety of embodiments, and such embodiments as may be construed to fall within the scope and meaning of the appended claims should be construed to be within the scope and intent of this invention.

Iclaim:

l. in a method oftreating wells wherein a treating agent is injected into'a formation through a zone in said well isolated from another section of said well by a formation packer set in the annulus between the wall of said well and the well tubing the steps of placing a sealing agent comprising a slurry of temporary bridging material in a hydrocarbon-soap gel in said well within said annulus on the low-pressure side of said packer, applying pressure to said sealing agent to force gel into the flow channels in said section on said low-pressure side of said packer and seal the flow channels around said packer between the high-pressure side of said packer and the low-pressure side of said packer, injecting said treating agent into said zone through said tubing, applying pressure to said treating agent to force it into said formation while maintaining a substantially equal pressure on said sealing agent and contacting said gel with a gel peptizer so that it willflow out of said flow channels and not subsequently deter production from said section of said well.

2. A method according to claim 1 in which said gel peptizer is incorporated in said gel whereby said gel is reduced after a time to substantially the viscosity of said hydrocarbon.

3. In a method of testing wells wherein Well fluids are withdrawn from a selected formation into a zone in said well isolated from a section of said well by a formation packer set in the annulus between the wall of said well and the well tubing the steps of placing a sealing agent comprising a slurry of temporary bridging material in a hydrocarbon gel on the high-pressure side of said packer in said section of said well, withdrawing said well fluid from said selected formation while maintaining a pressure on said gel at least as great as the .pressure in said zone, and contacting said gel with a gel peptizer, whereby the flow channels around said packer are sealed by said gel and well fluids from said selected formation are not contaminated by fluids from said section, and whereby fluid production from said section is not permanently plugged.

4. A method according to claim 3 in which said sealing agent is placed in said annulus and said well fluids are withdrawn from said selected formation through said tubing.

5. In a process of the class wherein a selected formation in a well having a tubing therein is treated by injecting fluids into or withdrawing fluids therefrom, said selected formation being in fluid communication through a common boundary with another section penetrated by said well, the steps of setting a packer at said boundary in the annulus between the wall of said well and said tubing, placing a sealing agent comprising slurry of temporary bridging material in a hydrocarbon gel in said annulus opposite said section, applying pressure to said sealing agent to force gel into the flow channels in said section allowing gelation of said gel in said flow channels to continue so that said gel cannot readily be displaced from and will seal the flow channels around said packer, treating said selected formation as above stated while said flow channels are sealed, and then contacting said gel with a gel peptizer so that said gel is removed from said flow channels and will not subsequently deter production from said section of said well.

6. A process according to claim 5 wherein substantially equal pressures are maintained on said fluids and on said sealing agent while treating said selected formation.

7. A process according to claim 5 in which said gel peptizer is incorporated in said gel whereby said gel is reduced after a time to substantially the viscosity of said hydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS 8 Reistle Apr. 3, 1951 Shinouda Feb. 5, 1952 Clark May 13, 1952 OTHER REFERENCES The Oil and Gas Journal, October 14, 1948, pages Acidizing Hand Book, Kingston, copyright 1947 by Gulf Publishing Company, pages 70-74 inclusive. 

1. IN A METHOD OF TREATING WELLS WHEREIN A TREATING AGENT IS INJECTED INTO A FORMATION THROUGH A ZONE IN SAID WELL ISOLATED FROM ANOTHER SECTION OF SAID WELL BY A FORMATION PACKER SET IN THE ANNULUS BETWEEN THE WALL OF SAID WELL AND THE WELL TUBING THE STEPS OF PLACING A SEALING AGENT COMPRISING A SLURRY OF TEMPORARY BRIDGING MATERIAL IN A HYDROCARBON-SOAP GEL IN SAID WELL WITHIN SAID ANNULUS ON THE LOW-PRESSURE SIDE OF SAID PACKER, APPLYING PRESSURE TO SAID SEALING AGENT TO FORCE GEL INTO THE FLOW CHANNELS IN SAID SECTION ON SAID LOW-PRESSURE SIDE OF SAID PACKER AND SEAL THE FLOW CHANNELS AROUND SAID PACKER BETWEEN THE HIGH-PRESSURE SIDE OF SAID PACKER AND THE LOW-PRESSURE SIDE OF SAID PACKER, INJECTING SAID TREATING AGENT INTO SAID ZONE THROUGH SAID TUBING, APPLYING PRESSURE TO SAID TREATING AGENT TO FORCE IT INTO SAID FORMATION WHILE MAINTAINING A SUBSTANTIALLY EQUAL PRESSURE ON SAID SEALING AGENT AND CONTACTING SAID GEL WITH A GEL PEPTIZER SO THAT IT WILL FLOW OUT OF SAID FLOW CHANNELS AND NOT SUBSEQUENTLY DETER PRODUCTION FROM SAID SECTION OF SAID WELL. 